* xpp: start splitting color functions
* xpp: split color functions in transform-specific files
* xpp: move YCoCgR functions for halide/simd
* xpp: update version to 0.3.0
* xpp: more unsigned type refactoring
* xpp: use XppStatus return type
* xpp: more XppStatus refactoring
* xpp: reduce macro usage in Halide generator
* xpp: cleanup Halide generator macro usage
* xpp: wrap standard memory functions
* xpp: start moving halide/simd declarations
* xpp: refactor simd files
* xpp: rename _c functions to _generic
* xpp: remove unused CopyFromRetina function
* xpp: wrap YCoCg-R function
* xpp: cleanup xpp singleton initialization
* xpp: add Halide RGB to YCoCgR conversion
* xpp: add Halide YCoCgRToRgb
* xpp: refactor Halide YCoCgR420